linux-kernel - [PATCH AUTOSEL 6.8 13/25] wifi: iwlwifi: read txq->read

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Date: Sun,  7 Apr 2024 09:11:01 -0400
From: Sasha Levin <sashal@...nel.org>
To: linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Cc: Johannes Berg <johannes.berg@...el.com>,
	Miri Korenblit <miriam.rachel.korenblit@...el.com>,
	Sasha Levin <sashal@...nel.org>,
	kvalo@...nel.org,
	gregory.greenman@...el.com,
	kuba@...nel.org,
	pagadala.yesu.anjaneyulu@...el.com,
	linux-wireless@...r.kernel.org
Subject: [PATCH AUTOSEL 6.8 13/25] wifi: iwlwifi: read txq->read_ptr under lock

From: Johannes Berg <johannes.berg@...el.com>

[ Upstream commit c2ace6300600c634553657785dfe5ea0ed688ac2 ]

If we read txq->read_ptr without lock, we can read the same
value twice, then obtain the lock, and reclaim from there
to two different places, but crucially reclaim the same
entry twice, resulting in the WARN_ONCE() a little later.
Fix that by reading txq->read_ptr under lock.

Signed-off-by: Johannes Berg <johannes.berg@...el.com>
Signed-off-by: Miri Korenblit <miriam.rachel.korenblit@...el.com>
Link: https://msgid.link/20240319100755.bf4c62196504.I978a7ca56c6bd6f1bf42c15aa923ba03366a840b@changeid
Signed-off-by: Johannes Berg <johannes.berg@...el.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/net/wireless/intel/iwlwifi/queue/tx.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/wireless/intel/iwlwifi/queue/tx.c b/drivers/net/wireless/intel/iwlwifi/queue/tx.c
index ca74b1b63cac1..0efa304904bd3 100644
--- a/drivers/net/wireless/intel/iwlwifi/queue/tx.c
+++ b/drivers/net/wireless/intel/iwlwifi/queue/tx.c
@@ -1588,9 +1588,9 @@ void iwl_txq_reclaim(struct iwl_trans *trans, int txq_id, int ssn,
 		return;
 
 	tfd_num = iwl_txq_get_cmd_index(txq, ssn);
-	read_ptr = iwl_txq_get_cmd_index(txq, txq->read_ptr);
 
 	spin_lock_bh(&txq->lock);
+	read_ptr = iwl_txq_get_cmd_index(txq, txq->read_ptr);
 
 	if (!test_bit(txq_id, trans->txqs.queue_used)) {
 		IWL_DEBUG_TX_QUEUES(trans, "Q %d inactive - ignoring idx %d\n",
-- 
2.43.0